1. Field of the Invention
The present invention relates generally to toy vehicles with drive motors, such as electric motors, and more specifically, to a toy vehicle having an automatic transmission for downshifting and upshifting automatically in response to changes in terrain or other loads placed on the vehicle.
2. Description of the Related Art
In the art of motorized toy vehicles, in the ordinary case, the vehicle has an axle driven by an electric motor (battery powered) through a transmission which essentially acts as a speed reducer. The transmission is usually geared for operation at a single gear ratio (the ratio of the engine rotational speed to the drive axle rotational speed).
An automatic shifting mechanism for a toy vehicle is described in Japanese Kokoku 54-35148. The transmission described therein enables the vehicle to either stop operation or run automatically in the event of the vehicle encountering an obstruction or some other external force which impedes motion of the vehicle. The transmission includes a pair of gears cooperatively and operatively interrelated such that one gear has a notch which receives a boss projecting from an opposing surface of the other gear. When a load is applied to the vehicle, the boss which was previously engaged with the notch is forced outwardly to cause the gear having the boss to move axially apart from the gear having the notch to effectively produce a shifted transmission.
The aforementioned shifting mechanism is suitable for a vehicle striking an obstacle but it is not very effective for a vehicle which is designed to run over obstacles, for example, for an off-road type toy vehicle.